Paper surfaces under the microscopic view are observed to be formed by intertwisted wood fibers. Such structures of paper surfaces are unique from one location to another and are almost impossible to duplicate. Previous work used microscopic surface normals to characterize such intrinsic structures as a “fingerprint” of paper for security and forensic applications. In this work, we examine several key research questions of feature extraction in both scientific and engineering aspects to facilitate the deployment of paper surface-based authentication when flatbed scanners are used as the acquisition device. We analytically show that, under the unique optical setup of flatbed scanners, the specular reflection does not play a role in norm map estimation. We verify, using a larger dataset than prior work, that the scanner-acquired norm maps, although blurred, are consistent with those measured by confocal microscopes. We confirm that, when choosing an authentication feature, high spatial-frequency subbands of the heightmap are more powerful than the norm map. Finally, we show that it is possible to empirically calculate the physical dimensions of the paper patch needed to achieve a certain authentication performance in equal error rate (EER). We analytically show that log(EER) is decreasing linearly in the edge length of a paper patch.

中文翻译：

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使用平板扫描仪进行纸张表面认证的微观结构估计


在显微镜下观察，纸张表面是由交织的木纤维形成的。这种纸张表面的结构从一个地方到另一个地方都是独一无二的，几乎不可能复制。以前的工作使用微观表面法线来表征这种内在结构，作为安全和法医应用的纸张“指纹”。在这项工作中，我们研究了科学和工程方面特征提取的几个关键研究问题，以便在使用平板扫描仪作为采集设备时促进基于纸张表面的身份验证的部署。我们分析表明，在平板扫描仪独特的光学设置下，镜面反射在范数图估计中不起作用。我们使用比之前的工作更大的数据集验证扫描仪获取的范数图虽然模糊，但与共焦显微镜测量的结果一致。我们确认，在选择身份验证特征时，高度图的高空间频率子带比范数图更强大。最后，我们证明可以凭经验计算在等错误率（EER）下实现一定认证性能所需的纸片的物理尺寸。我们分析表明 log(EER) 在纸片的边缘长度上呈线性减小。